1. Field of the Invention
The present invention relates in general to a process for the production of a phosphorus removal aggregate that is highly advantageous for removal of phosphorus from waste or storm water and more specifically concerns the production of such material from a fractionating sand mine waste product.
2. Description of the Prior Art
The prior art related to this subject matter is essentially divided into three different areas. First, stabilization of naturally occurring clay deposits for the general purpose of rendering them suitable load bearing soils, second, the production of lightweight aggregate materials from a variety of naturally occurring raw material and third, the mechanical incorporation of carbonates of calcium or magnesium in the aggregate material.
The literature describing stabilization of naturally occurring clays directed to the application or for the purpose of increasing soil stability is differentiated from the process and products of the present invention in that in such described applications, in-situ clays are never removed from their natural location and stabilization occurs through the creation of load bearing columns in one case, or in others, the creation of a load bearing crust within the top several inches or feet of the body to be stabilized. Such applications, by their very nature, are designed to facilitate the construction of roads or other structures in areas where this type of construction would otherwise be prohibited or at a minimum require the costly removal of the subsurface clay body and subsequent replacement with suitable construction quality soil.
In the case of the prior literature on the subject of manufacturing lightweight aggregate materials, it is important to note that the above process of the present invention is differentiated from other lightweight aggregate production processes in several significant ways. Traditional lightweight aggregates are produced by mining or otherwise extracting a natural deposit of clay which contains inherently incorporated organic matter, and firing that material in a rotary kiln. As such, the final product characteristics are dependent on the composition and make-up of the original clay deposit. The mining of natural deposits of clay produces as a starting material a clay of approximately 60%-80% solids, which starting material is thus suitable for immediate pyro-processing. However, it does have many disadvantages typically associated with the mining and extraction of naturally occurring mineral deposits including, but not limited to the remediation of the mining area, ecological disturbance, and the disposal of waste products.
The process of this invention, however, has none of those disadvantages. The starting material is itself a byproduct of mining activity. The use of such byproduct reduces the environmental impact of the mining activity in that were it not converted to a beneficial use product, it would require disposal in impoundment. As such, the process and associated products of this invention qualify as “green” products because as a result of their manufacture, environmental consequences are significantly reduced. In addition, the final products of the invention are capable of a degree of customization not available within the range of naturally produced lightweight aggregates. Products with greater mechanical strength, products with lower bulk density, products with greater insulating properties, than any product currently produced from naturally occurring clay deposits can be produced by use of the present invention with none of the environmental consequences normally associated with the production of lightweight aggregates from naturally occurring clay deposits.
The phosphorus removal aspect of this invention is novel over what is found in the prior art which consists of essentially using furnace slags naturally high in calcium or using man-made aggregates produced by the addition of limestone or calcium carbonate. Addition of either of these two materials would be a non starter in the instant process because they do not provide the initial dehydration provided by the addition of calcium oxide, a necessary element of such process. The initial dehydration or stabilization of the clay of this invention facilitates the additional processing into the various forms.
In the production of the phosphorus removal aggregate of the present invention, the only limitation on how much CaO can be incorporated is mechanical. The more CaO added, the more difficult it is to mechanically incorporate the CaO. However, the more CaO incorporated, the higher the sorption capacity the aggregate has for phosphorus.
One of the more relevant patents of the prior art is U.S. Pat. No. 6,627,083 B2 issued Sep. 30, 2003. But, the process disclosed therein differs from the present invention in that the clay it utilizes is a natural organic clay deposit in which carbonates of calcium or magnesium are incorporated as flux material. In contrast, the clay of the present invention does not contain any natural organic material, and as such is not by nature an expanding clay as the term is utilized generally in the production of lightweight aggregate materials. Further, the CaO thought to be bound or encapsulated in the ceramic matrix of the aggregate remains available to react with soluble phosphorus present in waste or storm water. In fact, the surprising result is that approximately 85% of the CaO is available to react, despite its encapsulation in the aggregate matrix.